As a semiconductor device used for a purpose such as power control, there can be cited MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Some of such MOSFET have a super junction structure in which n-type semiconductor regions and p-type semiconductor regions are alternately provided via respective trenches. The MOSFET having such a structure is provided with the trenches high in aspect ratio due to the miniaturization of the pitch of the cells, and has a problem of improving easiness of filling the trenches in addition to protection of the semiconductor regions.